West Lafayette, Indiana
October 4, 2007
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A fungus called Fusarium
graminearum causes head blight, or scab,
which causes more damage to cereal grains than
any other disease. Purdue molecular biologist
Jin-Rong Xu is using the fungus' genome to find
ways to prevent it. The laboratory dish on the
left shows the pathogenic fungus that attacks
wheat, barley and some other small grains. The
right dish shows Fusarium graminearum
that has been genetically modified so that it
won't cause the disease. (Purdue Agricultural
Communication photo/Tom Campbell) |
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Why a pathogen is a pathogen may
be answered as scientists study the recently mapped genetic
makeup of a fungus that spawns the worst cereal grains disease
known and also can produce toxins potentially fatal to people
and livestock.
The fungus, which is especially destructive to wheat and barley,
has resulted in an estimated $10 billion in damage to U.S. crops
over the past 10 years. The scientists who sequenced the fungus'
genes said that the genome will help them discover what makes
this particular pathogen so harmful, what triggers the process
that spreads the fungus and why various fungi attack specific
plants.
These investigations also may lead to producing plants that are
completely resistant to the fungus Fusarium graminearum,
something that hasn't been possible previously, said Jin-Rong
Xu, a Purdue University
molecular biologist. He is pinpointing which genes enable the
fungus to cause the disease Fusarium head blight, or scab.
In a recent issue of the journal Science, Xu and an
international scientific team reported that certain chromosomal
regions in Fusarium graminearum appear to dictate plant and
fungus molecular interactions that allow the fungus to
contaminate crops and cause disease.
The researchers located all of the genes on the fungus'
chromosomes and then determined the genes' chemical makeup, or
sequence.
"The Fusarium graminearum genome was easy to assemble because,
unlike other fungal genomes, there aren't too many repetitive
DNA sequences," Xu said. "It seems that this Fusarium can
efficiently detect and remove duplicated sequences or
transposable elements, which kept the genome clean and
well-organized."
This basic information on the Fusarium graminearum genome will
aid in further research and also provide information on other
fungi and their interaction with plants, he said.
"Because we now have the genome sequence and a microarray
containing the whole genome, it will help us determine what
genes allow this fungus to behave as it does," Xu said. "It also
will make it easier to identify and determine the function of
similar genes in other pathogens and their plant interactions."
Fusarium graminearum, which exists worldwide, cuts crop yield,
damages grain quality and produces mycotoxins. The fungus caused
a widespread head blight epidemic during the 1990s in wheat- and
barley-growing regions around the world. Experts estimate that
from 1998 to 2000 the central and northern Great Plains of the
United States suffered economic losses of $2.7 billion due to
the disease. In Indiana alone in 1996, the fungus caused at
least $38 million in crop loss, according to the USDA.
The mycotoxins caused by the fungus can affect people and
livestock that ingest infected grain. Pigs, cattle, horses,
poultry and people can develop vomiting, loss of appetite,
diarrhea, staggering, skin irritation and immunosuppression. The
most severe cases can be fatal.
Some scientific evidence suggests that these toxins cause
cancer. People in developing countries are at the greatest risk
of eating grain contaminated with Fusarium mycotoxins. Although
not all types of Fusarium cause disease and produce toxins,
those types that do infect other crops, including corn and hay.
Currently, fungicides aren't effective because the fungus only
attacks during the beginning of the plants' flowering stage.
It's difficult to gauge the precise time to spray, and it's
expensive to try to protect the crops over a long period. The
fungus can survive through the winter in crop remnants left in
fields as natural mulch.
The pathogen is most likely to appear and cause infection in
early spring when the weather is warm and humid or rainy. By the
time Fusarium contamination is noticeable on plants, head blight
has already damaged the grain.
Xu is searching for the genes involved in the infection process.
"We are using the whole-genome microarray of Fusarium
graminearum to identify the genes that are functional during
plant infection," Xu said. "We are looking at the biochemical
signaling pathways that influence whether a gene is turned on or
off. This will help us find ways to develop new, stable and
environmentally safe ways to prevent these infections."
Xu was one of the co-applicants for a $1.9 million grant from a
U.S. Department of Agriculture/National Science Foundation
partnership that funded the genome project. The endeavor was
headed by Corby Kistler, a USDA-Agricultural Research Service
geneticist based at the University of Minnesota.
Christina Cuomo of the Broad Institute at the Massachusetts
Institute of Technology led the sequencing. Other members of the
research team included scientists from Michigan State
University; Cornell University; Pacific Northwest National
Laboratory; University of Arizona; St. Louis University;
University of Tennessee; and institutions in Germany, Canada,
Austria, England, France, Ukraine and the Netherlands.
Writer: Susan A. Steeves |
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